One method successfully updates the array within the data function, while a separate method continues to find the array empty

Question

One method successfully updates the array within the data function, while a separate method continues to find the array empty

I am facing an issue in my app where I need to update an array. The process involves fetching data from the database and adding it to the array, which works fine. However, when I try to use this updated array in another method, it seems that the array is not being updated.

Interestingly, when I inspect the exerciseList array in the DOM, I can see the data. But when I check the length of the array inside the getExercises function, it still shows 0. It appears as though the method is being executed before the data is actually added to the array.

Any thoughts on why this might be happening?

data: () => ({
    exerciseList: []

});

created() {
    this.getDataBaseCollection("Exercise", this.exerciseList); // Array gets populated here
}
mounted() {
    this.getExercises();
},

methods: {
    getDataBaseCollection: function (CollectionName, list) {
        db.collection(CollectionName).onSnapshot(snapshot => {
            snapshot.forEach(doc => {
                list.push(doc.data());
            });
        });

    },

    getExercises: function () {
        console.log(this.exerciseList.length);  // Length is still 0 even though the array should have data
    }
 },

javascript arrays vue.js vuejs2 vue-component

Answer 1

Answer №1

It appears that an important aspect to address is updating the component's exerciseList variable, as opposed to the list argument. These two variables are distinct - objects are passed by reference while arrays are passed to functions by value, making list its own independent variable from excerciseList. Below is some rough code demonstrating how to ensure exerciseList is properly updated and how to monitor when all values have been added to the array.

// include exerciseListLoaded to flag when all data is ready
data: () => ({
    exerciseList: [],
    exerciseListLoaded: false
});

created() {
    this.getDataBaseCollection("Exercise"); // information populates the array here
}
mounted() {
    // timing of `onSnapshot` callback relative to `mounted` being called may result in 0
    console.log("Mounted");
    this.getExercises();
},

watch: {
    // watch for all data being ready
    exerciseListLoaded () {
       console.log("All Loaded");
       this.getExercises();
    }
},

methods: {
    // update the exerciseList on the component
    getDataBaseCollection: function (CollectionName) {
        // handle `this` carefully within `onSnapshot`, as it might change within that function
        const componentScope = this;
        db.collection(CollectionName).onSnapshot(snapshot => {
            snapshot.forEach(doc => {
                componentScope.exerciseList.push(doc.data());
                // can also update `list` here if necessary
            });
            // setting this triggers actions in the component once all data is loaded via the `watch` config
            componentScope.exerciseListLoaded = true;
        });

    },

    getExercises: function () {
        console.log(this.exerciseList.length);  // length showing as 0? Seems like the array is empty
    }
 },

Answer 2

It appears that an important aspect to address is updating the component's exerciseList variable, as opposed to the list argument. These two variables are distinct - objects are passed by reference while arrays are passed to functions by value, making list its own independent variable from excerciseList. Below is some rough code demonstrating how to ensure exerciseList is properly updated and how to monitor when all values have been added to the array.

// include exerciseListLoaded to flag when all data is ready
data: () => ({
    exerciseList: [],
    exerciseListLoaded: false
});

created() {
    this.getDataBaseCollection("Exercise"); // information populates the array here
}
mounted() {
    // timing of `onSnapshot` callback relative to `mounted` being called may result in 0
    console.log("Mounted");
    this.getExercises();
},

watch: {
    // watch for all data being ready
    exerciseListLoaded () {
       console.log("All Loaded");
       this.getExercises();
    }
},

methods: {
    // update the exerciseList on the component
    getDataBaseCollection: function (CollectionName) {
        // handle `this` carefully within `onSnapshot`, as it might change within that function
        const componentScope = this;
        db.collection(CollectionName).onSnapshot(snapshot => {
            snapshot.forEach(doc => {
                componentScope.exerciseList.push(doc.data());
                // can also update `list` here if necessary
            });
            // setting this triggers actions in the component once all data is loaded via the `watch` config
            componentScope.exerciseListLoaded = true;
        });

    },

    getExercises: function () {
        console.log(this.exerciseList.length);  // length showing as 0? Seems like the array is empty
    }
 },

Answer 3

Answer №2

When employing this within a function, it points to the function itself rather than the Vue instance. You can utilize the following approach:

fetchActivities() {
        console.log(this.activityList.length);  
    }

Answer 4

When employing this within a function, it points to the function itself rather than the Vue instance. You can utilize the following approach:

fetchActivities() {
        console.log(this.activityList.length);  
    }

One method successfully updates the array within the data function, while a separate method continues to find the array empty

Answer №1

Answer №2

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